A year on Mars — more to come

Press, 17 November 1977, Page 17

A year on Mars — more to come

The lonely Viking-2 laboratory, one of its spidery legs perched on top of a rock and most of its energy being used to keep itself warm, is now in its fourteenth month on the enigmatic red planet. Mars. Viking-2, ending its first y ear on the rock-strewn plains of Utopia, and its sister craft, Viking-1, which landed in the Basin of Chryse 7500 kilometres to the south-east on July 20. 1976, have taken 70 samples of soil and rock for processing and analysis in their miniature biological, organic, and inorganic chemistrv laboratories, and some 2500 pictures in colour, black and white, infra-red, and stereoptically. But the question of life on Mars remains unresolved: the life-seeking experiments, their supplies

exhausted, have been permanently turned off. It is the recent weather on Mars that scientists are mostly talking about. Two global dust storms enveloped the planet, performing a global weather experiment. As a result, scientists observing the effects of dust in the simpler atmospheric and weather system of Mars, feel they will better be able to predict the effects of dust — and similar atmospheric pollutants — on the weather and surface temperatures of Earth. The question has been: What will be the longrange effects on Earth of increasing amounts of industrial pollution, such as particles similar to dust? Some scientists have believed that industrial and volcanic dust would cool the surface of blocking sunlight; others have maintained that particle pollution would heat the surface, because the dust would first absorb solar heat, then reradiate it to the ground. “The Martian answer — as a result of studying two dust storms — is that dust heats the atmosphere and changes weather patterns, but cools the surface,” says Dr Ichtiaque Rasool, scientist at the National Aeronautics and Space Administration. With the dust from the storm clearing out of the Martian skies, the two orbiters that brought the landers to Mars will begin their second year of mapping the surface. Among the scheduled activities in the second year for the two landers is “gardening.” The soil sampler arms will dig rows and troughs in the soil, providing scientists with information about the physical and magnetic properties of the Martian soil. The one operational seismometer on Viking-2 will continue monitoring the planet for Marsquakes to compare with two such “events” registered earlier. Don Anderson, chief of the Earthquake Laboratory at the California Institute of Technology, is now convinced that he has seen the results of only one Marsquake — a magnitude “three” event that occurred within 200 kilometres of the lander site.

The experiment that analyses the chemical composition of the soil — found to be similar to earth’s desert soil, with iron, calcium, silicon, titanium, aluminium, sulphur, and chlorine — will continue searching for trace elements such as rubidium and strontium, which so far have been found — if at all — in very low concentrations. The landers’

atmospheric experiments that detected oxygen, nitrogen, krypton, and xenon in the air have been turned off. It has been the Martian winter and weather, especially the dust storms, that, like weather on earth, have been making the most news recently.

The first dust storm began in mid-February, when it was spring in the Martian southern hemisphere and autumn in the north where the two Vikings sit. The storm began just south of the equator. The two circling orbiters photographed and tracked its evolution. “It took only 10 days to cover the whole planet,” says Dr Geoffrey Briggs of the National Aeronautics and Space Administration. “Still photographs taken at the lander sites revealed no dust being kicked up. But the orbiter pictures showed tremendous amounts of turbulence and activity all over the planet.” Soon, the entire globe was shrouded in dust.

The atmosphere finally cleared by mid-May, but then during the first week of June, early winter in the north, and early summer in the south, another storm began. (Martian seasons are all six months long because its “year” around the sun takes two earth vears).

The dust had several measurable effects on the weather. Atmospheric temperatures increased. Shortly before the June

By

EVERLY DRISCOLL,

I.P.S. science writer

storm, the orbiters measued temperatures at about 25 kilometres altitude above the wintery North Pole at minus 138 degress Celsius (minus 216 degrees F). The dust raised the temperatures to minus 81 degrees C (minus 114 degrees F) — some 60 degrees. By late July, with the dust settling, the temperatures returned to their original values.

The North Pole at the time was in the dark of polar night in winter. “The increases in temperatures must have been the result of the transport of energy in the atmosphere from the lower (equatorial) regions," says Dr Frank Palluconi. of the Jet Propulsion Laboratory, where the Vikings are monitored. Farther south, atmospheric dust had absorbed solar heat, raising air tem-

peratures but blocking sunlight from the surface. At the two landing sites, the surface temperatures fell — at Viking-2 by an average 10 degrees — and the atmospheric pressures rose. At the Viking-1 site, surface pressures rose from 7.8 to 8.0 millibars. The dust also darkened the Martian skies blocking about 50 per cent of the sun’s light, according to

N.A.S.A.’s Dr Robert Henry.

But a meteorologist, James Tillman, of the University of Washington at Seattle, saw dark skies over Mars for another reason — a passing weather front. On February 16, two days before the start of the first dust storm, the cameras on Viking-2 took a prescheduled picture which clearly showed the landscape. Two hours later, in another picture, the landscape was almost invisible, says Dr Tillman. At the same time, it became colder, atmospherics rose, and the winds from the south shifted to the south-west, then came from the northwest, then from the north. What Dr Tillman saw, he believes, was the north “polar hood” moving down over the landing site. The polar hood is a cloud of carbon dioxide and water that accumulates over the North Pole in the fall. As. temperatures fall in winter, the carbon dioxide and water condense to ice and fall to

the ground forming part of the winter polar cap. Viking-2 sits about 360 kilometres to the south of the most southerly extension of the cap in winter. The carbon dioxide and water come from the South Pole where, since it is summer, the cap melts, and the material evaporates and moves to the north where it condenses. So far, the Viking orbiters have been able to observe one part of this yearlycycle — winter at the South Pole, the melting of the southern cap, summer. and the formation of the winter cap in the nonh. The dust storm, scientists think, has affected this cycle of material from the south to the north. As ice forms on the poles, the dust in the air, mixed with the carbon dioxide and water, is also deposited at the poles, forming a new layer each polar winter.

Visible on photographs are results of thousands of years of this deposition — layers upon layers of dust and frozen water and carbon dioxide, stacked like saucers of different sizes in a pile.

While the orbiters photographed this air movement, the two landers recorded the atmospheric circulation as changes in surface pressures. At the Viking-2 site, where the pressures are normally around 8.0 millibars, they rose to 10.8 millibars at the peak of winter.

The worst of the winter is over. The skies have cleared from the June dust storm and the sun is steadily moving northward. Spring will come to the northern hemisphere this month. Flight controllers at the J.P.L., with their hands full operating the Voyager-2 spacecraft, now on its way to Jupiter, and Voyager-1, which was launched on September 5, are also scheduling the reactivation of both Vikings for their second year on Mars.